1. Field of the Invention
This invention relates to mechanical seals, more particularly to rotating mechanical shaft seals.
2. Description of the Prior Art
In mechanical end face seals, sealing is effected by maintaining a pair of sealing faces, both normal to the shaft axis, in full face contact. In order to achieve optimum reliability and face life, the faces must remain in constant alignment, with controlled and predictable face loading to insure proper fluid film thickness between the faces. Exact alignment and loading must be obtained at the time of sealed installation and maintained during all operating conditions. Alignment and loading must be controlled in the event of either imperfect shaft location at installation or shaft displacement relative to the stationary portion of the equipment to be sealed during operation. These displacements are categorized as either axial, radial or angular. A shaft may possibly exhibit only one form of displacement, but typically all three forms exist to some degree in practical application.
Self-contained cartridge type seals, incorporating all critical components in a preassembled unit, are known to the prior art. At installation, true self-contained cartridge type design accomplishes correct spring loading of the faces by virtue of being preassembled, and compensates for static axial and radial shaft displacements since the cartridge sleeve axial position is predetermining, and the centering clip design typical of the art insures that the stationary portion of the seal is centered with respect to the shaft and the rotating sleeve of the cartridge. Cartridge type seal construction has not been heretofore utilized as a part of a design comparable to this invention. The problem of radial shaft deflections in operation is addressed in the existing art by designing the harder mating face of the pair of faces with a greater outside diameter and lesser inside diameter than the soft face. The intent is to achieve proper face contact in the event of radial displacement of the shaft by providing an extended contact area. Additionally, in the existing art, it is known to spring load one or more of the both seal faces, to provide axial and angular mobility, in an attempt to compensate for initial angular misalignment, and for axial and angular shaft displacements in operation. Additionally, it is known to incorporate an anti-friction bearing integrally in a rigidly matted mechanical seal and housing, as an effort to stabilize the rotating shaft against displacements in the seal area. It is a common characteristic of sealed designs of the prior art that in the case of relative axial, radial or angular displacement between the rotating shaft and the stationary portion of the equipment to be sealed, a corresponding displacement takes place between the rotating end and stationary portions of the seal because of their separate and individual rigid attachment to the rotating shaft and stationary equipment respectively.
Such prior art attempts have not been entirely successful at compensating for shaft displacements. In operation, radial displacement produces uneven wear and tends to introduce any abrasive particles present to the sealed interface in the case of wider hard faces. With flexibility mounted, spring loaded faces, face pressures do to the variations in spring compression with axial or angular shaft displacements can have a disadvantageous effect upon the life and performance of the seal due to over compression, under compression and assymetric compression of the faces. Additionally, successive spring compression due to axial shaft displacement can lead to localized over stress and distortion of the mating faces, especially in the case where the spring load effect is completely negated by bottoming the spring. With a design incorporating a bearing unit with the seal, some shaft stabilization may be achieved, but this is typically only in the radial mode, and often the bearing transmits excessive loads to the sealed cavity, resulting in possible deformation of the stationary seal components. This invention respresents an advance to the state-of-the-art because it overcomes the above noted undesirable conditions by providing a seal which requires no critical measurements at installation, is self-centering and self-aligning, and which maintains optimum face alignment and loading, without face distortion, in the event of static or dynamic shaft displacement in any plane.
Examples of previously known forms of seal and bearing structures including some of the general structural and operational features of the instant invention are disclosed in U.S. Pat. Nos. 2,470,419, 2,513,079, 3,019,779, 3,186,721, 3,612,390, 3,963,247, 4,093,324 and 4,272,084.